U.S. patent number 9,042,516 [Application Number 13/647,423] was granted by the patent office on 2015-05-26 for nondestructive examination of structures having embedded particles.
This patent grant is currently assigned to The Boeing Company. The grantee listed for this patent is The Boeing Company. Invention is credited to Robert B. Greegor, James A. Grossnickle.
United States Patent |
9,042,516 |
Grossnickle , et
al. |
May 26, 2015 |
Nondestructive examination of structures having embedded
particles
Abstract
A system comprises a structure having particles embedded at a
level within the structure, and X-ray imaging apparatus for
capturing images of the particles at the level.
Inventors: |
Grossnickle; James A.
(Bellevue, WA), Greegor; Robert B. (Auburn, WA) |
Applicant: |
Name |
City |
State |
Country |
Type |
The Boeing Company |
Chicago |
N/A |
IL |
|
|
Assignee: |
The Boeing Company (Chicago,
IL)
|
Family
ID: |
49354440 |
Appl.
No.: |
13/647,423 |
Filed: |
October 9, 2012 |
Prior Publication Data
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|
Document
Identifier |
Publication Date |
|
US 20140098936 A1 |
Apr 10, 2014 |
|
Current U.S.
Class: |
378/58; 378/62;
378/44 |
Current CPC
Class: |
G01N
23/087 (20130101); Y10T 428/24917 (20150115); G01N
2223/615 (20130101); G01N 2223/607 (20130101) |
Current International
Class: |
G01N
23/04 (20060101) |
Field of
Search: |
;378/58 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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103 22 055 |
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Dec 2004 |
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DE |
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06-155583 |
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Jun 1997 |
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JP |
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WO2009032809 |
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Mar 2009 |
|
WO |
|
Other References
Chen et al., "Metal-bonded Co-Ferrite Composites for
Magnetostrictive Torque Sensor Applications" IEEE Transactions on
Magnetics, vol. 35, No. 5, (Sep. 1999), pp. 3652-3654. cited by
applicant .
Chen et al.,"Health monitoring of composites embedded with
magnetostrictive thick film without disassembly," Inst. of Physics
Publishing, SmartMater.Struct.15(2006) 20-32. cited by applicant
.
Grimes et al., "Wireless Magnetoelastic Resonance Sensors: A
Critical Review" Sensors 2002, 2, 294-313. cited by applicant .
Pasquale et al., "Stress sensing with Cobased ferrite composites,"
Journal of Magnetism and Magnetic Materials 242-245 (2002)
1460-1463. cited by applicant .
Saravanos et al., "Detection of Delaminations in Composite Beams
Using Piezoelectric Sensors," NASA Technical Memorandum 106611
(Jun. 1994). cited by applicant .
Tan et al.,"Delamination Detection of a Laminated Beam Using
Magnetostrictive Composite Sensor and Actuator," Journ. of
Reinforced Plastics & Composites, 26-8 (2007) 831-46. cited by
applicant .
Jordan et al. "Microradiographic strain measurement using markers,"
Experimental Mechanics, vol. 34, No. 2, Jun. 1994, pp. 155-165.
cited by applicant .
Germnaneau et al. "Comparison between X-ray micro-computed
tomography and optical scanning tomography for full strain
measurement by digital volume correlation," NDT&E
International, vol. 41, No. 6, Sep. 2008, pp. 407-415. cited by
applicant .
Bay et al., "Digital volume correlation: three-dimensional strain
mapping using X-ray tomography," vol. 39, No. 3, Sep. 1999, pp.
217-226. cited by applicant.
|
Primary Examiner: Johnston; Phillip A
Attorney, Agent or Firm: Gortler; Hugh P.
Claims
The invention claimed is:
1. A system comprising a structure having particles embedded at
different levels within the structure, wherein the particles at the
different levels differ by at least one of nominal size and
composition; X-ray imaging apparatus for capturing images of the
particles; and a computer programmed to analyze the images to
determine strains at different locations at the different
levels.
2. The system of claim 1, further comprising identifying internal
structural inconsistencies from the strains.
3. The system of claim 1, wherein determining the strains includes
forming pixel blocks containing the particles, and determining
changes in shape of the pixel blocks.
4. The system of claim 1, wherein the computer is programmed to
perform digital image correlation of the particles in the
images.
5. The system of claim 1, wherein the imaging apparatus includes
first and second X-ray sources on one side of the structure and at
least one X-ray detector on an opposite side of the structure.
6. The system of claim 1, wherein the particles are arranged in a
non-uniform, irregular pattern.
7. The system of claim 1, wherein the particles are metal
particles.
8. The system of claim 1, wherein the structure includes first and
second members joined by a layer of adhesive, the adhesive layer
containing a pattern of the particles.
9. The system of claim 1, wherein the structure includes a laminate
and wherein the particles are embedded in at least two plies of the
laminate.
10. The system of claim 1, wherein the structure includes a
plurality of plies of reinforcing fibers embedded in a matrix; and
wherein the different levels are formed by the plurality of plies;
whereby different types of the particles are embedded in different
plies within the structure.
11. A method of performing nondestructive examination on a
structure having embedded particles, the particles embedded at a
level within the structure, the method comprising: Illuminating the
structure with X-rays; forming an image of the illuminated
structure, the image showing the particles; determining
displacements of the particles in the image; and determining
strains from the displacements.
12. The method of claim 11, wherein the particles are illuminated
to fluoresce, scatter, or absorb the X-rays.
13. The method of claim 11, wherein determining the displacements
includes determining shape changes of pixel blocks in the
image.
14. The method of claim 11, wherein forming the image includes
using, first and second detectors at an angle with respect to the
particles to create depth in the image.
15. The method of claim 11, wherein a computer is used to perform
digital image correlation (DIC) to determine the displacement of
the particles.
16. The method of claim 14, further comprising identifying internal
structural inconsistencies from the strains.
17. The method of claim 11, wherein the particles are embedded in
multiple plies, wherein the particles embedded in the different
plies differ by the nominal size and/or composition; wherein the
different plies having embedded particles are illuminated at
different X-ray energy levels; and wherein the displacement of the
particles in the image is determined for each ply having embedded
particles.
18. The method of claim 11, wherein the particles are embedded in
different plies, wherein the particles embedded in the different
plies differ by the nominal size and/or composition; wherein the
different plies having embedded particles are illuminated to
fluoresce, and wherein forming the image includes using energy
dispersive detection to image the fluorescing particles.
19. A laminate comprising a plurality of plies of reinforcing
fibers in a matrix, the matrix containing patterns of metal
particles embedded within different plies, wherein the particles
embedded in the different plies differ by at least one of nominal
size and composition.
20. The laminate of claim 19, wherein the particles embedded in the
different plies differ by composition.
21. The laminate of claim 19, wherein the particles embedded in the
different plies are arranged in non-uniform, irregular patterns.
Description
BACKGROUND
Nondestructive examination (NDE) may be used to evaluate properties
of composite structures. For instance, NDE such as ultrasonic
testing may reveal internal structural inconsistencies such as
voids, wrinkles, cracks and delaminations.
However, ultrasonic testing does not reveal internal strains within
composite structures. Other techniques may determine strains at the
surface or bulk of composite structures, but not within the
composite structures.
It would be desirable to nondestructively determine strains within
composite structures.
SUMMARY
According to an embodiment herein, a system comprises a structure
having particles embedded at a level within the structure, and
X-ray imaging apparatus for capturing images of the particles at
the level.
According to another embodiment herein, a method of performing
nondestructive examination on a structure having embedded particles
comprises illuminating the structure with X-rays; forming an image
of the illuminated structure, the image showing the particles; and
determining displacements of the particles in the image.
According to another embodiment herein, a laminate comprises a
plurality of plies of reinforcing fibers in a matrix. The matrix
contains patterns of metal particles embedded within different
plies, wherein the particles embedded in the different plies differ
by at least one of nominal size and composition.
These features and functions may be achieved independently in
various embodiments or may be combined in other embodiments.
Further details of the embodiments can be seen with reference to
the following description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration of a structure including embedded
particles.
FIGS. 2A and 2B are illustrations of particles embedded within a
structure before and after the structure has undergone stress.
FIG. 3 is an illustration of a method of determining strain within
a structure having embedded particles.
FIG. 4 is an illustration of a system for determining strain within
a structure having embedded particles.
FIG. 5 is an illustration of a method of using the system of FIG.
4.
FIG. 6 is an illustration of a multi-ply structure including
embedded particles at multiple levels.
FIG. 7 is an illustration of a method of fabricating and
nondestructively examining a CFRP laminate.
DETAILED DESCRIPTION
Reference is made to FIG. 1, which illustrates a structure 110
including embedded particles. In some embodiments, the structure
110 may be a composite laminate composed of a plurality of plies of
reinforcing fibers embedded in a matrix. For instance, the laminate
may include multiple plies of carbon reinforcing fibers embedded in
a plastic matrix. In FIG. 1, each element 112 represents multiple
plies. In other embodiments, the structure 110 may include two or
more members 112 (e.g., rigid composite members) that are
adhesively bonded together at a bond line.
The particles are embedded at a level 114 below a surface of the
structure 110. As shown in FIG. 1, the level 114 is at a depth (d)
below the surface. For a structure 110 including members 112
adhesively bonded together at a bond line, the particles may be
embedded in the bond line. That is, the bond line is at a depth (d)
below the surface. For a structure 110 including a plurality of
laminated plies 112, the particles may be embedded in one or more
of the plies. That is, the ply or plies containing the embedded
particles are a depth (d) below the surface.
The embedded particles are made of a material that is not
completely transparent to X-rays. For instance, the embedded
particles may fluoresce, scatter or absorb X-rays. In some
embodiments, the particles may be metal particles. The particles
may be micron-sized or smaller.
Reference is now made to FIG. 2A, which shows a plurality of
embedded particles 210. The particles 210 are arranged in a pattern
that is non-uniform and irregular. In some embodiments, the
particles 210 may be arranged in clumps. In other embodiments, the
particles 210 may be arranged in a stochastic pattern. For example,
the particles 210 may be arranged in a stochastic speckle
pattern.
The structure 110 may undergo stress from external forces and/or
internal forces (e.g., by temperature cycling). The stress causes
strain in the structure 110. In laminates made of composite fiber
reinforced plastic (CFRP), for instance, the strain may cause
deformations or internal inconsistencies such as voids, wrinkles,
cracks and delaminations.
Reference is now made to FIG. 3, which illustrates a method of
determining strains within a structure having particles embedded
particles therein, where the particles are not completely
transparent to X-rays. At block 310, the structure is illuminated
with X-rays. Except for the particles, the structure may fully
transmit the X-rays. The particles prevent the X-rays from being
fully transmitted. For instance, the particles may fluoresce,
scatter or absorb the X-rays, or they may reflect the X-rays (e.g.,
at grazing incidence).
At block 320, an image of the illuminated structure is formed. The
image shows a pattern of particles at a level within the
structure.
At block 330, the image is processed to determine displacements of
the particles at different locations at the level. At block 340,
strains are computed from the displacements.
Reference is made to FIGS. 2A and 2B, which illustrate particles
210 embedded at a level within the structure 110. Assume FIG. 2A is
a baseline image of the particles 210 prior to the structure 110
undergoing stress, and assume FIG. 2B is an image of the particles
after the structure 110 has undergone stress. A pixel block 220
encompasses several particles 210. Notice the skewing of the pixel
block 220 in FIG. 2B. The skewing indicates that the particles 210
within the pixel block 220 have been displaced as a result of the
stress.
Displacements and strains may be computed by digital image
correlation (DIC). DIC is an optical method that employs tracking
and image registration techniques for accurate measurements of
changes in images. DIC may perform pattern recognition on multiple
images. Each image may be broken up into blocks of pixels (e.g.,
15.times.15 pixel blocks, 25.times.25 pixel blocks 15.times.20
pixel blocks) that cover a certain number (e.g., five to seven)
particles. These blocks of pixels are found in all of the images,
and then the shape of each pixel block in each image is determined.
The change of shape of each block of pixels determines a
displacement at a location at the level. In this manner,
displacements are determined at different locations at the
level.
A set of strains may then be computed at each block center. A
strain field for the level may be formulated as a matrix of the
strains. Interior modulus properties may also be determined from
stress versus strain curves in the elastic region of the
material.
Reference is now made to FIG. 4, which illustrates a system 410 for
determining strains at a level within a structure 110, where
particles are embedded at that level. The system 410 includes
imaging apparatus 420 for capturing images of the particles within
the structure 110. The imaging apparatus 420 of FIG. 4 includes
first and second X-ray sources 422 and first and second X-ray
detectors 424. The sources 422 may provide collimated X-rays. If
the particles block the X-rays, the detectors may include
semiconductor detectors that convert X-rays to electrical signals
or semiconductor detectors that convert X-rays to visible light,
which is then converted to electric signals. If the particles
fluoresce in response to the X-rays, the image may be formed by
energy dispersive detection.
High contrast in the images is desirable. Distances between the
sources 422, the structure 110, and the detectors 424 may be
adjusted to give the proper field of view and best contrast.
The first and second detectors 424 may be oriented at an angle with
respect to the particles to create depth perception in the images.
Depth perception, in turn, enables structural inconsistencies such
as internal delaminations to be identified.
A system herein is not limited to two detectors. Some embodiments
may include only a single detector. Others may include more than
two detectors.
The system 410 further includes a computer 430 programmed to
process the images created by the detectors 424. The processing
includes digital image correlation of the pixel blocks of particles
within the images. The computer 430 may be programmed with a
commercial off the shelf DIC software, such as ARAMIS software.
In some embodiments, the computer 430 may be further programmed to
identify internal structural inconsistencies from the strain field.
For example, the strain field may be compared to baseline data
corresponding to different types of structural inconsistencies. In
other embodiments, skilled technicians may analyze the strain field
to identify structural inconsistencies.
FIG. 5 is an illustration of a method of using the system of FIG. 4
to perform nondestructive inspection on a structure having
particles embedded at a level. At block 510, the computer 430
accesses a baseline image of the structure. The baseline image
represents a "healthy" structure. The baseline image may be been
taken before the structure was placed into service, or it may be
taken at a later time after having been stressed.
At block 520, the computer 430 commands the imaging apparatus 420
to capture one or more images of the particles within the structure
110. At block 530, the computer 430 processes the captured and
baseline images to detect displacement of a number of pixel blocks
at each level. Several pixel blocks may be used to determine the
value of displacement at a given location.
At block 540, the computer 430 determines strains from the pixel
block displacements, and formulates a strain field at the level. If
the structure 110 includes two parts bonded together at a bond
line, and the particles are embedded in the bond line, then a
strain field would be determined at the level of the bond line. If
the structure 110 is a laminate, and one of the plies is embedded
with particles, then a strain field would be determined at the
level of that ply.
At block 550, the strain field is used to identify internal
structural inconsistencies such as voids, wrinkles, delaminations
and cracks. For example, a delamination would manifest as a change
in out of plane displacement (in a 3D image), while a crack or
wrinkle would manifest as a large localized strain.
A structure herein is not limited to particles at a single level.
In some embodiments, a structure may include particles embedded at
multiple levels.
FIG. 6 is an illustration of a laminate 610 including metal
particles embedded at multiple levels. Different types of particles
are embedded in different plies. The type of particle may differ by
nominal size and/or composition. As but one example, one ply 612
may be embedded with copper particles, another ply 614 may be
embedded with titanium particles, another ply 616 with aluminum
particles, and so on. Other metals include, but are not limited to,
gold, silver, tungsten, and iron. Other plies 618 of the structure
do not contain particles that affect the X-rays.
FIG. 6 shows every other layer being imbedded with metal particles.
In practice however, there may be greater separation between plies
having embedded particles. As but one example, in a laminate having
thirty plies, one of every six plies may contain metal
particles.
Reference is now made to FIG. 7, which illustrates the fabrication
and nondestructive examination of a CFRP laminate. Prior to layup,
the different plies of the laminate are pre-impregnated with resins
having different types of particles dispersed therein (block 710).
Those plies not containing particles are impregnated with resin.
During layup of the laminate (block 720), the pre-impregnated plies
may be deposited on a forming tool.
After the layup has been cured (block 730), nondestructive
examination is performed. During nondestructive examination, the
laminate is illuminated with X-rays and the particles at different
levels are imaged (block 740). In some embodiments, the levels may
be illuminated sequentially at different X-ray energy levels,
thereby creating images of different levels. In other embodiments,
the different levels may be illuminated and imaged in a single
pass. Particles at different levels may be differentiated by the
amount of energy they absorb. For example, lead particles will
absorb more energy than titanium particles and, consequently, will
have a lower grayscale value in the image.
In other embodiments, the different particles absorb the X-rays and
fluoresce at different frequencies. Images of the different levels
may be formed by energy dispersive detection, which would allow
discrimination of the florescent spectra of the different
particles. For example, the florescent spectra of titanium, copper,
tungsten, and lead are dispersed at different levels.
Using DIC, the displacement of the metal particles in the image is
determined at different locations for each of the different levels
(block 750). Strain fields are computed for the different levels
(block 760).
* * * * *